Riva grate & ride plate joint.

I noticed a slight loss in top speed while keeping the same rpm recently. I removed my riva grate to seal up the shoe & when I put the grate back on I noticed the ride plate is 1mm lower than the grate on 1 side (about 3/4" long) of the grate. everything is flush except that one spot. That wasn't there before I know that. Would this actually make a difference in top speed?